Not Applicable
The present invention relates generally to bellows seals, and more specifically to bellows seals having low vibration transmissibility.
In semiconductor processing, exposure apparatuses are commonly used to transfer images from a reticle onto semiconductor wafers. Typical exposure apparatuses include a support frame, a measurement system, a control system, an illumination source, an optical device, a reticle stage for retaining a reticle, and a wafer stage for retaining a semiconductor wafer. The reticle stage, wafer stage and the optical device are commonly contained within separate enclosures or chambers to reduce the chances of cross-contamination, reduce the time required to purge each enclosure after accessing, and to improve system modularity.
The size of the features within the images transferred onto the wafers from the reticle are extremely small. Accordingly, the relative positioning of the reticle stage and wafer stage to the optical device is critical to the manufacturing of high density, semiconductor wafers. Therefore, exposure apparatuses are very sensitive to vibrations, which can move the stages out of precise relative alignment. Sources of mechanical vibrations are located both inside and outside of the exposure apparatuses. For example, the reticle stage can generate reaction forces that vibrate the wafer stage, and vice-versa, which may cause relative misalignment between the stages. Each of these stages can also vibrate and cause misalignment of the optical device. Floor vibrations can also vibrate exposure apparatuses. In addition to affecting the alignment of the exposure apparatuses, mechanical vibrations can cause the measurement system to improperly measure the positions of the stages relative to the optical device. Also, vibration of the optical device can cause deformations of the lens elements within, thereby degrading the optical imaging quality.
Currently, the exposure apparatus enclosures containing the reticle stage, wafer stage and optical device are commonly connected to each other through conventional bellows seals and scrunched bellows seals. See FIG. 1, which provides a side plan view of a conventional bellows seal 100 having a height, H, and a diameter, D. See FIG. 2A, which provides a side plan view of a scrunched bellows seal 200 having a height, H, and a diameter, D. FIG. 2B illustrates a pre-scrunched bellows seal before becoming scrunched into the configuration shown in FIG. 2A. Directional reference arrows are also illustrated to show the six possible degrees-of-freedom. Both conventional bellows seals and scrunched bellows seals are stiff in twisting (about the axial direction, "THgr"z) and translational (in the radial direction, x or y) motions when the diameter of the seals, D, is much larger than the height of the seals, H. This relationship of diameter versus height is common since exposure apparatus enclosures generally have large openings and are positioned closely together. Unfortunately, the stiffness of these bellows seals allow vibration to be more easily transmitted through the seals from one enclosure to the next. As discussed above, such transmission of vibration causes misalignment, measurement and deformation problems. A further disadvantage regarding the conventional bellows seal 100 is that expensive tooling is required to form each of the pleats 102. A further disadvantage of the scrunched bellows seal 200 is that the buckling of the random pleats tend to cause mirco-vibrations and non-deterministic, discontinuous reaction forces during motion.
In view of the foregoing, an improved seal for connecting separate enclosures that allows for a reduced amount of vibration to be transmitted through the seal would be desirable.
The present invention pertains to a double bellows type seal that can provide a passageway between enclosed chambers. These chambers may be chambers containing semiconductor-manufacturing equipment. The significance of the inventive double bellows seal is such that its high degree of flexibility in all six degrees of freedom greatly minimizes the amount of vibration that may pass from one chamber to the other. This flexibility is especially critical in semiconductor manufacturing environments where mechanical vibrations may disturb the finely adjusted alignment between various chambers. The combination of two bellows also substantially eliminates any tendencies of the seal to impose rotational and translational forces upon each of the chambers during seal movements. In one embodiment of the present invention, the flexible double bellows seal includes a plurality of rings including first and second end rings, a middle ring, a first bellows, and a second bellows. The first bellows is formed from a flexible material that is sealingly connected between the first end ring and the middle ring, and it has a twist bias in a first rotational direction relative to an axis of the rings. The second bellows is formed from a flexible material that is sealingly connected between the second end ring and the middle ring. The second bellows has a twist bias in a second rotational direction relative to an axis of the rings that is opposite that of the first rotational direction. In addition to minimizing the transmission of vibration between the enclosures that the double bellows seal connects, the helical pleats of the bellows are relatively easy to manufacture.
Another aspect of the present invention relates to a photolithography system that utilizes the double bellows seal. This photolithography system includes a reticle stage contained within a first chamber, an optical device contained within a second chamber, a wafer stage contained within a third chamber, and a first and second double bellows seal as described in the preceding paragraph. The first double bellows seal connects the first and second chambers and the second double bellows seal connects the second and third chambers.